Remove override of IReparseableElementType.isParsable (#30)

See https://github.com/JetBrains/intellij-community/blob/888c7be55e65f3a86e4939bb53fe4f1335af3cf0/platform/core-api/src/com/intellij/psi/tree/IReparseableElementType.java#L72

Author: jwren

third_party/src/main/java/com/jetbrains/lang/dart/DartTokenTypesSets.java

@@ -239,11 +239,6 @@ public DartLazyParseableBlockElementType() {
       super("LAZY_PARSEABLE_BLOCK", DartLanguage.INSTANCE);
     }
 
-    @Override
-    public boolean isParsable(final @NotNull CharSequence buffer, final @NotNull Language fileLanguage, final @NotNull Project project) {
-      return PsiBuilderUtil.hasProperBraceBalance(buffer, new DartLexer(), LBRACE, RBRACE);
-    }
-
     @Override
     public @Nullable ASTNode createNode(final @NotNull CharSequence text) {
       return new DartLazyParseableBlockImpl(this, text);